Secure bios mechanism in a trusted computing system

ABSTRACT

An apparatus including a ROM and a microprocessor. The ROM includes BIOS contents that are stored as plaintext and an encrypted digest. The encrypted digest includes an encrypted version of a first digest corresponding to the BIOS contents. The microprocessor is coupled to the BIOS ROM, and includes a tamper timer and a tamper detector. The tamper timer periodically generates an interrupt at a prescribed interval. The tamper detector accesses the BIOS contents and the encrypted digest upon assertion of the interrupt, and directs the microprocessor to generate a second digest corresponding to the BIOS contents and a decrypted digest corresponding to the encrypted digest using the same algorithms and key that were employed to generate the first digest and the encrypted digest, and compares the second digest with the decrypted digest, and precludes operation of the microprocessor if the second digest and the decrypted digest are not equal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending U.S. patentapplications, each of which has a common assignee and common inventors.

SERIAL FILING NUMBER DATE TITLE (CNTR.2629) XX/XX/XXXX APPARATUS ANDMETHOD FOR SECURING BIOS IN A TRUSTED COMPUTING SYSTEM (CNTR.2634)XX/XX/XXXX EVENT-BASED APPARATUS AND METHOD FOR SECURING BIOS IN ATRUSTED COMPUTING SYSTEM DURING EXECUTION (CNTR.2635) XX/XX/XXXXPARTITION-BASED APPARATUS AND METHOD FOR SECURING BIOS IN A TRUSTEDCOMPUTING SYSTEM DURING EXECUTION (CNTR.2636) XX/XX/XXXX SECURE BIOSTAMPER PROTECTION MECHANISM

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to the field of microelectronics, andmore particularly to an apparatus and method for securing a BasicInput/Output System (BIOS) in a computing system.

2. Description of the Related Art

Computing platforms come in all shapes and sizes. Desktop computers,laptop computers, tablet computers, personal digital assistants, andsmart phones and just a few of the many different forms taken on bythese very powerful tools.

When stripped down, virtually all of the forms of computing platformsshare the same basic architecture, or configuration. At the core is acentral processing unit (most often a microprocessor), memory forprogram storage (in the form of a hard disk or solid state disk), fastermemory from which the programs are executed (typically random accessmemory), and memory in which a basic input/output system (BIOS) isstored.

The BIOS is the lowest level of layered programming for these platformsand enables standard operating systems and application programs toperform operations using the hardware that is specific to a givencomputing platform configuration. The BIOS generalizes the myriad numberof particulars associated with hardware interfaces so that when changesare made to the platform configuration, higher level programs need notbe modified to accommodate the changes. Rather, the BIOS is typicallyupgraded when changes are made, which is why its storage is typicallyseparate from storage for the operating system and application programs.

Not only does BIOS include the basic operations of the given computingplatform, but it also includes configuration data and security data(such as whether the given computing system is authorized to executecertain application programs, etc.). Because BIOS contains securitydata, it is typically a target for hackers and the like. By modifying asystem's BIOS, for example, an unauthorized user may be able to executeprograms without a license. Thus, it is extremely important to systemdesigners that the validity and integrity of BIOS be protected andensured, when the system is not operating and when it is operating.

So, on the one hand it is desirable to provide easy access to a system'sBIOS in order to support upgrades and/or reprogramming to support systemconfiguration changes. And on the other hand it is important to protector restrict access to BIOS contents to preclude tampering byunauthorized parties.

Some attempts at achieving one or both of the above objectives haveresulted in mechanisms that are limiting. For example, moving BIOSstorage onto the same die as the system's microprocessor protects itfrom tampering, yet totally defeats the ease of upgrade objectivebecause the BIOS no longer is physically accessible. Other techniquesresort to encryption of BIOS contents, which is advantageous from aprotection perspective, but which cripple the performance of a systembecause of the unacceptable number of operations that are required todecrypt BIOS contents each time it is used.

Accordingly, what is needed is a novel technique that supportsaccessibility and upgrade of a computing system's BIOS contents, butwhich also protects those contents from unauthorized tampering.

SUMMARY OF THE INVENTION

The present invention, among other applications, is directed to solvingthe above-noted problems and addresses other problems, disadvantages,and limitations of the prior art.

The present invention provides a superior technique for protecting acomputing system from attacks on its BIOS. In one embodiment, anapparatus for protecting a basic input/output system (BIOS) in acomputing system is provided. The apparatus includes a BIOS read onlymemory (ROM), a tamper timer, and a tamper detector. The BIOS ROM hasBIOS contents and an encrypted message digest. The BIOS contents arestored as plaintext. The encrypted message digest includes an encryptedversion of a first message digest that corresponds to the BIOS contents.The tamper timer is configured to periodically generate a BIOS checkinterrupt that interrupts normal operation of the computing system at aprescribed interval. The tamper detector is operatively coupled to theBIOS ROM, and is configured to access the BIOS contents and theencrypted message digest upon assertion of the BIOS check interrupt, andis configured to direct a microprocessor to generate a second messagedigest corresponding to the BIOS contents and a decrypted message digestcorresponding to the encrypted message digest using the same algorithmsand key that were employed to generate the first message digest and theencrypted message digest, and is configured to compare the secondmessage digest with the decrypted message digest, and is configured topreclude the operation of the microprocessor if the second messagedigest and the decrypted message digest are not equal.

One aspect of the present invention contemplates an apparatus forprotecting a basic input/output system (BIOS) in a computing system. Theapparatus has a BIOS read only memory (ROM) and a microprocessor. TheBIOS ROM includes BIOS contents that are stored as plaintext and anencrypted message digest, where the encrypted message digest includes anencrypted version of a first message digest that corresponds to the BIOScontents. The microprocessor is coupled to the BIOS ROM, and includes atamper timer and a tamper detector. The tamper timer is configured toperiodically generate a BIOS check interrupt that interrupts normaloperation of the computing system at a prescribed interval. The tamperdetector is operatively coupled to the BIOS ROM, and is configured toaccess the BIOS contents and the encrypted message digest upon assertionof the BIOS check interrupt, and is configured to direct themicroprocessor to generate a second message digest corresponding to theBIOS contents and a decrypted message digest corresponding to theencrypted message digest using the same algorithms and key that wereemployed to generate the first message digest and the encrypted messagedigest, and is configured to compare the second message digest with thedecrypted message digest, and configured to preclude the operation ofthe microprocessor if the second message digest and the decryptedmessage digest are not equal.

Another aspect of the present invention comprehends a method forprotecting a basic input/output system (BIOS) in a computing system. Themethod includes storing BIOS contents as plaintext in a BIOS ROM alongwith an encrypted message digest that comprises an encrypted version offirst message digest that corresponds to the BIOS contents; periodicallygenerating a BIOS check interrupt that interrupts normal operation ofthe computing system at a prescribed interval; upon assertion of theBIOS check interrupt, accessing the BIOS contents and the encryptedmessage digest, and generating a second message digest corresponding tothe BIOS contents and a decrypted message digest corresponding to thefirst encrypted message digest using the same algorithms and key thatwere employed to generate the first message digest and the encryptedmessage digest; comparing the second message digest with the decryptedmessage digest; and precluding operation of the microprocessor if thesecond message digest and the decrypted message digest are not equal.

Regarding industrial applicability, the present invention is implementedwithin a MICROPROCESSOR which may be used in a general purpose orspecial purpose computing device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the presentinvention will become better understood with regard to the followingdescription, and accompanying drawings where:

FIG. 1 is a block diagram illustrating physical components disposed onthe motherboard of a present day computing system;

FIG. 2 is a block diagram depicting how the components of FIG. 1 areinterconnected, and in particular how the present day computing systemis configured with respect to its BIOS;

FIG. 3 is a block diagram featuring a mechanism according to the presentinvention for securing the BIOS of a computing system;

FIG. 4 is a block diagram showing a periodic mechanism according to thepresent invention for securing the BIOS of a computing system;

FIG. 5 is a block diagram illustrating an event-based mechanismaccording to the present invention for securing the BIOS of a computingsystem;

FIG. 6 is a block diagram detailing a partition-based mechanismaccording to the present invention for securing the BIOS of a computingsystem; and

FIG. 7 is a block diagram showing a secure BIOS tamper protectionmechanism according to the present invention.

DETAILED DESCRIPTION

Exemplary and illustrative embodiments of the invention are describedbelow. In the interest of clarity, not all features of an actualimplementation are described in this specification, for those skilled inthe art will appreciate that in the development of any such actualembodiment, numerous implementation-specific decisions are made toachieve specific goals, such as compliance with system-related andbusiness related constraints, which vary from one implementation toanother. Furthermore, it will be appreciated that such a developmenteffort might be complex and time-consuming, but would nevertheless be aroutine undertaking for those of ordinary skill in the art having thebenefit of this disclosure. Various modifications to the preferredembodiment will be apparent to those skilled in the art, and the generalprinciples defined herein may be applied to other embodiments.Therefore, the present invention is not intended to be limited to theparticular embodiments shown and described herein, but is to be accordedthe widest scope consistent with the principles and novel featuresherein disclosed.

The present invention will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present invention with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present invention. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

DEFINITIONS

Integrated Circuit (IC): A set of electronic circuits fabricated on asmall piece of semiconductor material, typically silicon. An IC is alsoreferred to as a chip, a microchip, or a die.

Central Processing Unit (CPU): The electronic circuits (i.e.,“hardware”) that execute the instructions of a computer program (alsoknown as a “computer application” or “application”) by performingoperations on data that include arithmetic operations, logicaloperations, and input/output operations.

Microprocessor: An electronic device that functions as a CPU on a singleintegrated circuit. A microprocessor receives digital data as input,processes the data according to instructions fetched from a memory(either on-die or off-die), and generates results of operationsprescribed by the instructions as output. A general purposemicroprocessor may be employed in a desktop, mobile, or tablet computer,and is employed for uses such as computation, text editing, multimediadisplay, and Internet browsing. A microprocessor may also be disposed inan embedded system to control a wide variety of devices includingappliances, mobile telephones, smart phones, and industrial controldevices.

Multi-Core Processor: Also known as a multi-core microprocessor, amulti-core processor is a microprocessor having multiple CPUs (“cores”)fabricated on a single integrated circuit.

Instruction Set Architecture (ISA) or Instruction Set: A part of acomputer architecture related to programming that includes data types,instructions, registers, addressing modes, memory architecture,interrupt and exception handling, and input/output. An ISA includes aspecification of the set of opcodes (i.e., machine languageinstructions), and the native commands implemented by a particular CPU.

x86-Compatible Microprocessor: A microprocessor capable of executingcomputer applications that are programmed according to the x86 ISA.

Microcode: A term employed to refer to a plurality of microinstructions. A micro instruction (also referred to as a “nativeinstruction”) is an instruction at the level that a microprocessorsub-unit executes. Exemplary sub-units include integer units, floatingpoint units, MMX units, and load/store units. For example, microinstructions are directly executed by a reduced instruction set computer(RISC) microprocessor. For a complex instruction set computer (CISC)microprocessor such as an x86-compatible microprocessor, x86instructions are translated into associated micro instructions, and theassociated micro instructions are directly executed by a sub-unit orsub-units within the CISC microprocessor.

Fuse: A conductive structure typically arranged as a filament which canbe broken at select locations by applying a voltage across the filamentand/or current through the filament. Fuses may be deposited at specifiedareas across a die topography using well known fabrication techniques toproduce filaments at all potential programmable areas. A fuse structureis blown (or unblown) subsequent to fabrication to provide for desiredprogrammability of a corresponding device disposed on the die.

In view of the above background discussion on securing critical programsand data in a trusted computing system and associated techniquesemployed within present day systems to detect and/or preclude tamperingwith those programs and data, a discussion will now be presented withreference to FIGS. 1-2 of those techniques as regards the BIOS componentof a present day system. Following this, a discussion of the presentinvention will be presented with reference to FIGS. 3-7.

Referring to FIG. 1, a block diagram 100 is presented illustratingphysical components disposed on a motherboard 102 (also referred to as asystem board) of a present day computing system. The components includea microprocessor 102 (also known as a CPU, processor, processor chip,etc.), a volatile memory 104 (also referred to as random access memory(RAM)), a chipset 108 (also called a memory controller, a memory hub, aninput/output hub, or a bridge (e.g., Northbridge or Southbridge)), aBIOS read-only memory (ROM) 110 that is typically installed in a socket112, and a disk interface 114. The motherboard 102 is typicallyinstalled within a computer chassis (e.g., a desktop or laptop chassis,a cell phone chassis, a tablet computer chassis, a set top box chassis),along with other components (e.g., power supply) that are required tocomplete a particular computer configuration. As one skilled in the artwill appreciate, there are many additional components and elements(e.g., clock generator, fans, connectors, graphics processor, etc.) thatare mounted on a typical present day motherboard 102, and it is notedthat those additional component and elements are not shown for claritysake. One skilled will also appreciate that there are many differentvariants of the components 104, 106, 114, 108, 110, 112 shown in FIG. 1which may be disposed on a typical present day system board 102, and itis noted that those components 104, 106, 114, 108, 110, 112 shown arereferred to by their generally accepted names. It is sufficient for thisapplication to note that the microprocessor 104 is coupled to thedepicted components 106, 114, 108, 110, 112 via physical interfaces (notshown) on the motherboard 102, typically metal traces. It is also notedthat the socket 112 is provided on the motherboard 102 because the BIOSROM 110 is subject to relatively frequent replacement in the factoryand/or the field.

Turning now to FIG. 2, a block diagram 200 is presented depicting howthe components 104, 106, 114, 108, 110, 112 of FIG. 1 areinterconnected, and in particular how the present day computing systemis configured with respect to its Basic Input/Output System (BIOS). Theblock diagram 200 shows a microprocessor 204 that includes an on-chip(i.e., on-die) high-speed cache memory 230. The microprocessor 204 iscoupled to a slower random access memory 206 via a memory bus 216. Themicroprocessor 204 is also coupled to a chipset 208 via a system bus218, and the chipset 208 is coupled to a disk interface 214 and a BIOSread only memory (ROM) 210 via a disk interface bus 224 and ROM bus 220,respectively. The BIOS ROM 210 may be coupled via a BIOS programming bus222 to an optional BIOS programming interface (not shown). As oneskilled in the art will appreciate, variations of the configurationshown in FIG. 2 may include a chipset 208 that also provides forinterface to the RAM 206 over the system bus 218 as opposed to a directmemory bus 216, and that may also provide for other types of busses (notshown) for interfacing the microprocessor 204 to other types ofperipheral interfaces (e.g., PCI Express, graphics processors).

In operation, as one skilled in the art will appreciate, applicationprograms 234 such as MICROSOFT® WORD® are stored on a hard (orsolid-state) disk (not shown), which are accessed via the disk interface214. Because the hard disk is a relatively slow device, the applicationprograms 234, prior to execution, are typically transferred to theexternal RAM 206 and then portions of these programs 234 are cached forexecution by the microprocessor 204 in its internal cache memory 230.When instructions in the application programs 234 require that themicroprocessor 204 perform system level operations (e.g., saving adocument to disk), then instructions (e.g., a save request) fromoperating system software 232, which is also loaded from hard disk intothe RAM 206 and cached in internal cache 230, are executed by themicroprocessor 204. The operating system software 232 provides for amore general interface that enables the application programs 234 toperform system level functions without a specific knowledge of theconfiguration. The operating system software 232 also allows formultiple application programs 234 to execute simultaneously on themicroprocessor 204, and furthermore performs background operations toefficiently manage use of the RAM memory 206.

However, operating systems 232 are in fact a middle layer of softwarewithin a present day computing system. In order to actually interface tohardware in the computing system (e.g., the hard disk), the operatingsystem 232 must execute instructions in a BIOS 236 that is stored in theBIOS ROM 210. The BIOS 236 is typically a number of small programs thatare function as the lowest level of software in a computer system, andthat interface the operating system 232 to the hardware of the computersystem. Like the operating system 232, the BIOS 236 provides for ageneralized interface to the computer hardware that allows the operatingsystem 232 to access the hardware without a specific knowledge thereof.The BIOS 236 enables a system designer to make changes to the hardware(e.g., the hard disk, chipset 208, RAM 206) in the computer system,without requiring that the operating system 232 or application programs234 be modified. Yet, when such changes in configuration are introduced,the BIOS 236 must be updated, and this is why the socket 112 and/or BIOSprogramming bus 222 are provided on the motherboard 102. These featuresare provided to enable ease of replacement or reprogramming of the BIOSROM 210. In some configurations the BIOS ROM 210 can be reprogrammeddirectly over the BIOS ROM bus 220. Consequently, to allow formodification of the BIOS 236, virtually all present day computingsystems provide the mechanisms described above. The BIOS ROM 210 is aseparate component that is easily accessible for purposes ofreprogramming or replacement.

The BIOS 236 is a very important feature in all computing systemconfigurations because the instructions therein enable the applicationprograms 234 and operating systems 232 to directly interface with thehardware. In addition to providing for interface to system hardware, theBIOS 236 performs a number of other functions that are essential toproper operation of a system. For example, when the system is poweredup, a power-on self test program within the BIOS 236 is executed toperform hardware tests and to verify proper configuration and operationof the system. The BIOS 236 also includes programs that identify andassign system resources to newly installed devices. The BIOS 236 furtherincludes programs that load the operating system 232 from the hard diskinto the RAM 206, and that transfer system control to the operatingsystem 232. Finally, the BIOS 236 includes programs that detect andpreclude tampering with the computing system.

Because the BIOS 236 is critical to both the security of and properoperation of a computing system, it is often a primary target forhacking and other forms of unauthorized tampering. For example, manywell known operating systems include provisions for activation byequipment manufacturers that is based on the BIOS 236 within a givencomputing system, thus allowing the manufacturers to sell the givencomputing system with its operating system pre-installed. Typically, amarker (or “signature”) is programmed into a specific location the BIOS236 by the manufacturer, and when the operating system boots up, itreads that marker from the specific location in the BIOS 236 to confirmthat it is booting on an authorized system. If the marker is absent orincorrect, then the operating system will not boot.

The above example is one of many different types of security featuresthat are programmed into a present day BIOS 236, and the presentinventors note that it is beyond the scope of the present application toprovide an in depth discussion of BIOS security features. It issufficient herein to note that the protection of a system's BIOS 236 isa paramount concern for system designers, because it is a primary targetfor tampering. In the example above, the objective for a hacker would beto edit (e.g., reprogram) a BIOS 236 in order to make the givencomputing system appear as an authorized system to a protected operatingsystem, or to make changes to the BIOS such that the operating systemdetermines that it is running on an authorized system, when indeed it isnot.

As alluded to above, most present day BIOS ROMs 110 are separatecomponents on a motherboard 102 and they are installed in a socket 112,specifically to allow easy replacement when system hardware changesnecessitate changes to the BIOS 236. Thus, hacks like the one describedwould be essentially effortless in the absence of other securitymechanisms.

Consequently, system designers have developed many different techniquesto detect and preclude tampering with a system and with the applicationprograms 234 and/or operating systems 232 running on the system. Forexample, in U.S. Patent Publication No. 2005/0015749, Mittal et al.propose protecting software from tampering by providing a secure memorypartition and a microprocessor that includes cryptographic logic toencrypt and decrypt programs and data. However, since the BIOS residesin a separate memory space from system software, it cannot be protectedfrom tampering by any means other that moving it onto the same die asthe microprocessor, which thus defeats a requirement for easy updates ofthe BIOS through chip replacement.

In U.S. Pat. No. 7,831,839, Hatakeyama discloses a secure boot ROM thatincludes encrypted boot code (i.e., BIOS), and a processor that includesa hardware decryption unit. When the processor boots up, the encryptedBIOS is read into local memory in the microprocessor and the decryptionunit decrypts and authenticates the BIOS. If successful, then theprocessor enters a secure processing mode and all BIOS calls areexecuted thereafter from the local, on-die memory. While Hatakeyamaprovides a mechanism for protecting BIOS via encryption of its contents,it order to execute efficiently, on-die local memory must be provided tostore the decrypted BIOS, and as one skilled in the art will appreciate,most present day BIOS programs (including configuration data) aremegabytes in size. Thus, the present inventor has observed thatHatakeyama's approach to BIOS protection is disadvantageous becauseproviding megabytes of on-die local memory increases the size and powerconsumption of the microprocessor, it decreases the reliability of thepart, and its overall cost goes up.

Other techniques have been developed that rely upon encrypting all or aportion of the BIOS contents, which must be decrypted each time a BIOScall is made, and the present inventor has noted that such techniquesdegrade the performance of a computing system, particularly duringboot-up, because decryption is inherently a slow process, even whenemploying on-die cryptographic hardware. Thus, encrypting BIOS contentsis undesirable from a performance perspective.

Accordingly, all of the above techniques—markers, secure memorypartitions, on-die local BIOS memory, encrypted BIOS contents—fail toprovide the ease of access to a system's BIOS ROM while at the same timeminimizing performance impacts. Consequently, the present invention isprovided to overcome these limitations, and others, through theemployment of novel techniques that enable the use of physicallydistinct BIOS ROMs, which may be installed in sockets for ease ofupgrade, and that provide BIOS content (e.g., instructions and/orconfiguration data) which is unencrypted (i.e., plaintext), yet that arecapable of detecting tampering initially upon boot-up, and thereafterduring system operation, without noticeably degrading systemperformance. The present invention will now be discussed with referenceto FIGS. 3-7.

Turning to FIG. 3, a block diagram 300 is presented featuring amechanism according to the present invention for securing the BIOS of acomputing system. The diagram 300 illustrates elements of amicroprocessor (e.g., processor, CPU, etc.) according to the presentinvention that is disposed on a single die and packaged for mounting ona motherboard, as described above. In one embodiment, the microprocessoris compatible with the x86 architecture and capable of executing all ofthe instructions within the x86 instruction set. Another embodimentcontemplates a multi-core processor disposed on a single die. A furtherembodiment considers a virtual processing core, that is, the core is arepresentation of a physical processor to an operating system of alogical partition that uses shared processors. In order to teach thepresent invention, simplified and necessary elements of themicroprocessor that are relevant will be described in the followingparagraphs, recognizing that there are many other components (e.g.,load/store logic, cache memory, scheduling logic, etc.) therein whichare known to those skilled in the art.

The microprocessor includes fetch logic 302 that is coupled to atranslator 304 via bus 324. The translator 304 is coupled to executionlogic 306 via bus 326. The execution logic 306 includes a crypto/hashunit 308 that is coupled to key storage 310 via bus 322. Themicroprocessor also includes a bus interface 318 through which themicroprocessor interfaces to a chipset. The bus interface 318 is coupledto a reset controller 312 via bus 328. The reset controller 312 receivesa reset signal RESET and generates a shutdown signal SHUTDOWN. The resetcontroller 312 includes a tamper detector 314 that is coupled to a bootloader 316 via bus NOBOOT. The reset controller 312 is coupled to theexecution logic 306 via a tamper bus TBUS.

In operation, the fetch logic 302 is configured to fetch programinstructions (from application programs, operating systems, and BIOScached in memory) for execution. The program instructions are providedto the translator 304 over bus 324. The program instructions aretranslated by the translator 304 into one or more microinstructions thatare executed by one or more elements within the execution logic 306 toperform the operations specified by the program instructions. Themicroinstructions (also known as microcode or firmware) are unique tothe microprocessor and are not accessible at the package level.

Under normal operating conditions, the BIOS instructions andconfiguration data are paged and cached in virtual memory after boot-up,and are therefore fetched by the fetch logic 302 for execution. However,normal operation of the microprocessor occurs following a successfulreset and boot sequence. The reset controller 312 receives the resetsignal RESET and directs the execution logic 306 to executed microcodeto perform self-tests and to begin boot up of the system. To detect BIOStampering and to preclude unauthorized operation of a system withinwhich the microprocessor is disposed, the reset controller 312—prior toboot up—fetches all of the contents a BIOS ROM (not shown) via the businterface 318, and provides the contents to the execution logic 306 viaTBUS. In one embodiment, the contents of the BIOS ROM contain a digitalsignature (also known as a hash or message digest) stored at a specificlocation in the BIOS ROM. As one skilled in the art will appreciate,depending upon the specific hash algorithm that is employed, the digitalsignature that corresponds to a hash of the BIOS ROM (say, 4 Megabytesin size) is very small in size (e.g., 256 bits), and is unique to thespecific contents of the BIOS ROM. That is, if contents of the ROM arechanged, then a hash of the changed contents will result in a differentdigital signature.

Prior to storage in the BIOS ROM, the digital signature is encryptedusing a cryptographic key that is provided to the BIOS manufacturer bythe manufacturer of the microprocessor. The cryptographic key isprogrammed into the key storage 310 during fabrication of themicroprocessor and thereafter cannot be accessed via programinstructions. In one embodiment, the key is unique to themicroprocessor. In one embodiment, contents of the key storage 310 areaccessible exclusively by the crypto/hash unit 308 under control oftamper detection microcode. The tamper detection microcode directs thereset controller 312 to fetch the contents of the BIOS ROM, includingthe encrypted digital signature, and the contents are provided to theexecution logic 306 via TBUS. Therein, the tamper detection microcodedirects the crypto/hash unit 308 to perform a hash of the BIOS accordingto the hash algorithm that was used by the BIOS manufacturer to generatethe digital signature. In one embodiment, the hash algorithm may be theSecure Hash Algorithm (e.g., SHA-0, SHA-1, etc.). Other embodimentscontemplate use of any of numerous well known message digest algorithms.The tamper detection microcode also directs the crypto/hash unit 308 todecrypt the encrypted digital signature that was fetched from the BIOSROM using the key stored in the key storage 310. In one embodiment thecrypto/hash unit employs the Digital Encryption Standard (DES) algorithmto decrypt the key. Another embodiment contemplates use of the AdvancedEncryption Standard (AES) algorithm. Other embodiments employ any of thewell known cryptographic algorithms. The digital signature generated bythe crypto/hash unit 308, along with the decrypted digital signaturewhose encrypted version is stored a the specific location in the BIOSROM are provided to the tamper detector 314 via TBUS.

The tamper detector 314 compares the two digital signatures. If they areequal, then the tamper detector 314 directs the boot loader 316 via busNOBOOT to begin a normal boot sequence for the microprocessor. If thetwo signatures are not equal, then the tamper detector 314 assertssignal SHUTDOWN and directs the boot loader 316 to discontinue the bootsequence. The SHUTDOWN signal directs remaining elements of themicroprocessor to power down or otherwise enter a mode that precludesnormal operation.

Advantageously, each time the microprocessor is reset, operations areperformed according to the present invention that only requiredecryption of an encrypted message digest that is stored in the specificlocation in the BIOS ROM, that is, decryption of a, say, 256-bit stringas opposed to a 4 Megabyte string. In addition, the present inventionallows for use of plaintext BIOS instructions/data that are stored in aphysically accessible configuration, such as the configuration discussedabove with reference to FIGS. 1-2. Ease of BIOS update is preserved, andsystem performance is not degraded. Costly internal local memory forstoring decrypted BIOS is not required. Furthermore, the cryptographickey that is employed to encrypt the message digest for storage in theBIOS ROM cannot be accessed by program instructions. It can only beaccessed directly by the crypto/hash unit 308.

Now referring to FIG. 4, a block diagram 400 is presented showing aperiodic mechanism according to the present invention for securing theBIOS of a computing system. The mechanism of FIG. 3 is employed tosecure a system's BIOS upon boot up, but the present inventor hasobserved that it is also possible to tamper with the BIOS when thesystem is operating normally, and thus there is a need to secure theBIOS from hacks during operation of the system as well as upon power up.Accordingly, the periodic mechanism is provided to accomplish thisobjective.

The diagram 400 illustrates elements of a microprocessor according tothe present invention that is disposed on a single die and packaged formounting on a motherboard, as described above. In one embodiment, themicroprocessor is compatible with the x86 architecture and capable ofexecuting all of the instructions within the x86 instruction set.Another embodiment contemplates a multi-core processor disposed on asingle die. A further embodiment considers a virtual processing core,that is, the core is a representation of a physical processor to anoperating system of a logical partition that uses shared processors. Inorder to teach the present invention, simplified and necessary elementsof the microprocessor that are relevant will be described in thefollowing paragraphs, recognizing that there are many other components(e.g., load/store logic, cache memory, scheduling logic, etc.) thereinwhich are known to those skilled in the art.

The microprocessor includes fetch logic 402 that is coupled to atranslator 404 via bus 424. The translator 404 is coupled to executionlogic 406 via bus 426. The execution logic 406 includes a crypto/hashunit 408 that is coupled to key storage 410 via bus 422. The executionlogic 406 also includes a random number generator 430. Themicroprocessor also includes a bus interface 418 through which themicroprocessor interfaces to a chipset. The bus interface 418 is coupledto a reset controller 412 via bus 428. The reset controller 412 receivesa reset signal RESET and generates a shutdown signal SHUTDOWN. The resetcontroller 512 includes a tamper detector 414 that is coupled to a bootloader 416 via bus NOBOOT. The tamper detector 414 includes a tampertimer 432. The reset controller 412 is coupled to the execution logic406 via a tamper bus TBUS and a random number bus RBUS.

In operation, elements of the mechanism of FIG. 4 perform in a mannersubstantially similar to those like named elements of the mechanism ofFIG. 3. However, in addition to detecting BIOS tampers during a resetboot sequence, the mechanism of FIG. 4 also includes tamper detectionmicrocode and elements that periodically check the BIOS to determine ifit has been tampered with while the computing system is operating. Likethe cryptographic key, the tamper timer 432 cannot be accessed byprogram instructions, but exclusively by the tamper detector 414 andtamper detection microcode. In one embodiment, the tamper timer 432interrupts normal operation of the system at an interval which isestablished by the tamper detection microcode. In one embodiment, thisinterval is 1 millisecond, which is more than sufficient to detectphysical attempts to replace the BIOS ROM with a hacked BIOS ROM. The1-millisecond interval is also sufficient to detect attempts toreprogram an existing BIOS ROM. When interrupted at this interval, thecontroller 412 fetches all of the contents the BIOS ROM (not shown) viathe bus interface 418, and provides the contents to the execution logic406 via TBUS. The tamper detection microcode directs the resetcontroller 412 to fetch the contents of the BIOS ROM, including theencrypted digital signature, and the contents are provided to theexecution logic 406 via TBUS. Therein, the tamper detection microcodedirects the crypto/hash unit 408 to perform a hash of the BIOS accordingto the hash algorithm that was used by the BIOS manufacturer to generatethe digital signature. The tamper detection microcode also directs thecrypto/hash unit 408 to decrypt the encrypted digital signature that wasfetched from the BIOS ROM using the key stored in the key storage 410.The digital signature generated by the crypto/hash unit 408, along withthe decrypted digital signature whose encrypted version is stored a thespecific location in the BIOS ROM are provided to the tamper detector414 via TBUS.

The tamper detector 414 compares the two digital signatures. If they areequal, then the tamper detector 414 returns control of themicroprocessor to the point at which the timer interrupt occurred. Ifthe two signatures are not equal, then the tamper detector 414 assertssignal SHUTDOWN. The SHUTDOWN signal directs remaining elements of themicroprocessor to power down or otherwise enter a mode that precludesnormal operation.

In another embodiment, rather than employing a fixed interval for thetamper timer 432, at completion of a periodic BIOS hack check the tamperdetection microcode directs the random number generator 430 to generatea random number which is entered into the tamper timer 432 to set afollowing interval for a next BIOS hack check. In this manner, the timesat which hack checks are performed cannot be predicted and anticipated.

Like the mechanism of FIG. 3, the periodic mechanism of FIG. 4 performsoperations according to the present invention that only requiredecryption of an encrypted message digest that is stored in the specificlocation in the BIOS ROM, that is, decryption of, say, a 256-bit stringas opposed to a 4 Megabyte string. In addition, the periodic mechanismprotects a secure system from BIOS hacks during normal operation of thesystem.

Turning to FIG. 5, a block diagram 500 is presented illustrating anevent-based mechanism according to the present invention for securingthe BIOS of a computing system. The mechanism of FIG. 4 is provided asan alternative embodiment for securing a system's BIOS upon when thecomputing system is operating normally, but one which is based upon theoccurrence of events as opposed to the passing of time. Such events mayinclude, but are not limited to, hard disk access (or other form ofinput/output access), changes to virtual memory mapping (forconfigurations in which the mechanism may be employed in a virtualprocessing system), changes to processor speed, and other types ofevents that typically occur in a present day computing system.Accordingly, the event-based mechanism is provided to accomplish thisobjective.

The diagram 500 illustrates elements of a microprocessor according tothe present invention that is disposed on a single die and packaged formounting on a motherboard, as described above. In one embodiment, themicroprocessor is compatible with the x86 architecture and capable ofexecuting all of the instructions within the x86 instruction set.Another embodiment contemplates a multi-core processor disposed on asingle die. A further embodiment considers a virtual processing core,that is, the core is a representation of a physical processor to anoperating system of a logical partition that uses shared processors. Inorder to teach the present invention, simplified and necessary elementsof the microprocessor that are relevant will be described in thefollowing paragraphs, recognizing that there are many other components(e.g., load/store logic, cache memory, scheduling logic, etc.) thereinwhich are known to those skilled in the art.

The microprocessor includes fetch logic 502 that is coupled to atranslator 504 via bus 524. The translator 504 is coupled to executionlogic 506 via bus 526. The execution logic 506 includes a crypto/hashunit 508 that is coupled to key storage 510 via bus 522. The executionlogic 506 also includes a random number generator 530. Themicroprocessor also includes a bus interface 518 through which themicroprocessor interfaces to a chipset. The bus interface 518 is coupledto a reset controller 512 via bus 528. The reset controller 512 receivesa reset signal RESET and generates a shutdown signal SHUTDOWN. The resetcontroller 512 includes a tamper detector 514 that is coupled to a bootloader 516 via bus NOBOOT. The tamper detector 514 includes an eventdetector 542 that receives an input/output access signal I/O ACCESS, avirtual memory map change signal VMMAP, a processor speed change signalSPEED, and other event signal OTHER. The reset controller 512 is coupledto the execution logic 506 via a tamper bus TBUS and a random number busRBUS.

In operation, elements of the mechanism of FIG. 5 function in a mannersubstantially similar to those like named elements of the mechanisms ofFIGS. 3 and 4. However, in addition to detecting BIOS tampers during areset boot sequence, the mechanism of FIG. 4 also includes tamperdetection microcode and elements that examine the BIOS to determine ifit has been tampered with while the computing system is operating.Validity checks of the BIOS are based upon the occurrence of eventsrather than based upon time. The present inventor notes that there are anumber of events that regularly occur in a present day computing systemthat are executed by the microprocessor such as I/O accesses (to, say,the hard disk, or PCI Express), changes in core clock speed, operatingsystem calls, changes in system state, and etc. Hence, the signals thatare received by the event detector 542 are exemplary only and are notmeant to restrict the types of events that may be utilized to triggerBIOS checks that that shown in the diagram 500.

Like the cryptographic key, the event detector 542 cannot be accessedvia the execution of program instructions, but exclusively by the tamperdetector 514 and tamper detection microcode. In one embodiment, theevent detector 542 interrupts normal operation of the system when one ofthe above noted events occurs, as is indicated by assertion of one ofthe signals I/O ACCESS, VMMAP, SPEED, OTHER. In another embodiment, theevent detector 542 interrupts normal operation of the system when aplurality of one of the above noted events occurs. A further embodimentcontemplates interruption of normal operation when a plurality of theevents occur (such as an I/O access and a change in core clock speed).The selected events and the number of occurrences thereof is establishedby the tamper detection microcode. When interrupted, the controller 512fetches all of the contents the BIOS ROM (not shown) via the businterface 518, and provides the contents to the execution logic 506 viaTBUS. The tamper detection microcode directs the reset controller 512 tofetch the contents of the BIOS ROM, including the encrypted digitalsignature, and the contents are provided to the execution logic 506 viaTBUS. Therein, the tamper detection microcode directs the crypto/hashunit 508 to perform a hash of the BIOS according to the hash algorithmthat was used by the BIOS manufacturer to generate the digitalsignature. The tamper detection microcode also directs the crypto/hashunit 508 to decrypt the encrypted digital signature that was fetchedfrom the BIOS ROM using the key stored in the key storage 510. Thedigital signature generated by the crypto/hash unit 508, along with thedecrypted digital signature whose encrypted version is stored at thespecific location in the BIOS ROM are provided to the tamper detector514 via TBUS.

The tamper detector 514 compares the two digital signatures. If they areequal, then the tamper detector 514 returns control of themicroprocessor to the point at which the event-based interrupt occurred.If the two signatures are not equal, then the tamper detector 514asserts signal SHUTDOWN. The SHUTDOWN signal directs remaining elementsof the microprocessor to power down or otherwise enter a mode thatprecludes normal operation.

In another embodiment, rather than employing a fixed number of eventoccurrences for the event detector 542, at completion of a BIOS hackcheck the tamper detection microcode directs the random number generator530 to generate a random number which is entered into the event detector542 to establish a following number of events that must occur before anext BIOS hack check is performed. In this manner, the number of eventsthat occur with trigger hack checks cannot be predicted and precludedvia surreptitious applications executing on the microprocessor. In afurther embodiment, the random number is employed to vary the type ofevent that triggers the next BIOS hack check.

Like the mechanisms of FIGS. 3 and 4, the event-based mechanism of FIG.5 performs operations according to the present invention that onlyrequire decryption of an encrypted message digest that is stored in thespecific location in the BIOS ROM, that is, decryption of, say, a256-bit string (the encrypted message digest) as opposed to a 4 Megabytestring (e.g., the entire BIOS). In addition, the event-based mechanismprotects a secure system from BIOS hacks during normal operation of thesystem, where the number and types of events that trigger hack checkscannot be determined and forced.

Referring now to FIG. 6, a block diagram 600 is presented detailing apartition-based mechanism according to the present invention forsecuring the BIOS of a computing system. The mechanism of FIG. 6 isprovided as an another embodiment for securing a system's BIOS upon whenthe computing system is operating normally, but one which checks only asubset of the BIOS when triggered by either a tamper timer interrupt (asin the embodiment of FIG. 3) or a system event (as in the embodiment ofFIG. 4). Accordingly, the partition-based mechanism is provided for usein configurations where performance is relatively critical and, sinceonly a portion of the BIOS is checked at each trigger point, there isless on an impact on system performance.

In the embodiment of FIG. 6, the BIOS space is divided into a pluralityof partitions, each of which have a corresponding message digest that isencrypted and stored in corresponding location in the BIOS ROM. In oneembodiment, the partition size is the same for each of the plurality ofpartitions. In another embodiment, the plurality of partitions havedifferent sizes. In one embodiment, only one of the plurality ofpartitions is checked responsive to a BIOS check trigger (e.g., timerinterrupt of event occurrence). In another embodiment, more than one ofthe plurality of partitions is checked responsive to a BIOS checktrigger. In another embodiment, the number of the plurality ofpartitions that are checked responsive to a BIOS check trigger isdetermined by the tamper detection microcode (e.g., a repeating cycleof, say, 1-3-1-2).

The diagram 600 illustrates elements of a microprocessor according tothe present invention that is disposed on a single die and packaged formounting on a motherboard, as described above. In one embodiment, themicroprocessor is compatible with the x86 architecture and capable ofexecuting all of the instructions within the x86 instruction set.Another embodiment contemplates a multi-core processor disposed on asingle die. A further embodiment considers a virtual processing core,that is, the core is a representation of a physical processor to anoperating system of a logical partition that uses shared processors. Inorder to teach the present invention, simplified and necessary elementsof the microprocessor that are relevant will be described in thefollowing paragraphs, recognizing that there are many other components(e.g., load/store logic, cache memory, scheduling logic, etc.) thereinwhich are known to those skilled in the art.

The microprocessor includes fetch logic 602 that is coupled to atranslator 604 via bus 624. The translator 604 is coupled to executionlogic 606 via bus 626. The execution logic 606 includes a crypto/hashunit 608 that is coupled to key storage 610 via bus 622. The executionlogic 606 also includes a random number generator 630. Themicroprocessor also includes a bus interface 618 through which themicroprocessor interfaces to a chipset. The bus interface 618 is coupledto a reset controller 612 via bus 628. The reset controller 612 receivesa reset signal RESET and generates a shutdown signal SHUTDOWN. The resetcontroller 612 includes a tamper detector 614 that is coupled to a bootloader 616 via bus NOBOOT. The tamper detector 614 includes a partitionselector 652. The reset controller 612 is coupled to the execution logic606 via a tamper bus TBUS and a random number bus RBUS.

In operation, elements of the mechanism of FIG. 6 function in a mannersubstantially similar to those like named elements of the mechanisms ofFIGS. 3-5. However, in addition to detecting BIOS tampers during a resetboot sequence, the mechanism of FIG. 6 also includes tamper detectionmicrocode and elements that examine the BIOS to determine if it has beentampered with while the computing system is operating. Validity checksof the BIOS are based upon the occurrence of triggers as describedabove. Upon the occurrence of a trigger, the partition selector 652selects one or more of the plurality of partitions of the BIOS to bechecked for validity.

Like the cryptographic key, the partition selector 652 cannot beaccessed via the execution of program instructions, but exclusively bythe tamper detector 614 and tamper detection microcode. When a triggeroccurs, normal operation of the computing system is interrupted and thepartition selector direct the controller 612 to fetch the contents ofone or more of the plurality of partitions of the BIOS ROM (not shown)via the bus interface 618, which are provided to the execution logic 606via TBUS. The contents, including one or more of the correspondingencrypted digital signatures, are provided to the execution logic 606via TBUS. Therein, the tamper detection microcode directs thecrypto/hash unit 608 to perform a hash of the one or more of theplurality of partitions according to the hash algorithm that was used bythe BIOS manufacturer to generate the one or more digital signatures.The tamper detection microcode also directs the crypto/hash unit 608 todecrypt the one or more corresponding encrypted digital signatures thatwere fetched from the BIOS ROM using the key stored in the key storage610. The one or more digital signatures generated by the crypto/hashunit 608, along with the one or more decrypted digital signatures whoseencrypted versions are stored in one or more specific locations in theBIOS ROM are provided to the tamper detector 614 via TBUS.

The tamper detector 614 compares one or more pairs of the digitalsignatures. If all comparisons are equal, then the tamper detector 614returns control of the microprocessor to the point at which theevent-based interrupt occurred. If the signatures are not equal, thenthe tamper detector 614 asserts signal SHUTDOWN. The SHUTDOWN signaldirects remaining elements of the microprocessor to power down orotherwise enter a mode that precludes normal operation.

In another embodiment, rather than checking a fixed or cyclic number ofthe plurality of partitions, at completion of a BIOS hack check thetamper detection microcode directs the random number generator 630 togenerate a random number which is entered into the partition selector652 to establish a following number of partitions that are to be checkedduring a next BIOS hack check. In this manner, the number of partitionsthat are validated at check point triggers cannot be predicted andprecluded via surreptitious applications executing on themicroprocessor. In a different embodiment, the random number is employedto indicate a next one of the plurality of partitions to be checked.

Now referring to FIG. 7, a block diagram 700 is presented showing asecure BIOS tamper protection mechanism according to the presentinvention. The embodiment of FIG. 7 is provided as a comprehensiveconfiguration that not only performs a full check of a computingsystem's BIOS upon power up and reset, but that also provides for a fullprotection of the system's BIOS during operation in a manner thatcombines the use of the techniques described above with reference toFIGS. 4-6.

The diagram 700 illustrates elements of a microprocessor according tothe present invention that is disposed on a single die and packaged formounting on a motherboard, as described above. In one embodiment, themicroprocessor is compatible with the x86 architecture and capable ofexecuting all of the instructions within the x86 instruction set.Another embodiment contemplates a multi-core processor disposed on asingle die. A further embodiment considers a virtual processing core,that is, the core is a representation of a physical processor to anoperating system of a logical partition that uses shared processors. Inorder to teach the present invention, simplified and necessary elementsof the microprocessor that are relevant will be described in thefollowing paragraphs, recognizing that there are many other components(e.g., load/store logic, cache memory, scheduling logic, etc.) thereinwhich are known to those skilled in the art.

The microprocessor includes fetch logic 702 that is coupled to atranslator 704 via bus 724. The translator 704 is coupled to executionlogic 706 via bus 726. The execution logic 706 includes a crypto/hashunit 708 that is coupled to key storage 710 via bus 722. The executionlogic 706 also includes a random number generator 730. Themicroprocessor also includes a bus interface 718 through which themicroprocessor interfaces to a chipset. The bus interface 718 is coupledto a reset controller 712 via bus 728. The reset controller 712 receivesa reset signal RESET and generates a shutdown signal SHUTDOWN. The resetcontroller 712 includes a tamper detector 714 that is coupled to a bootloader 716 via bus NOBOOT. The tamper detector 614 includes a tampertimer 732, an event detector 742, and a partition selector 752. Theevent detector 742 receives an input/output access signal I/O ACCESS, avirtual memory map change signal VMMAP, a processor speed change signalSPEED, and other event signal OTHER. The reset controller 712 is coupledto the execution logic 706 via a tamper bus TBUS and a random number busRBUS.

In operation, elements of the mechanism of FIG. 7 function in a mannersubstantially similar to those like named elements of the mechanisms ofFIGS. 3-6. However, in addition to detecting BIOS tampers during a resetboot sequence, the mechanism of FIG. 7 also includes tamper detectionmicrocode and elements that examine the BIOS to determine if it has beentampered with while the computing system is operating. Validity checksof the BIOS are based upon the occurrence of a timer interrupt from thetamper timer 732 and event triggers as described with reference to FIG.5 above. Upon the occurrence of a timer interrupt or event trigger, thepartition selector 752 selects one or more of the plurality ofpartitions of the BIOS to be checked for validity as is discussed abovewith reference to FIG. 6.

The tamper timer 732, the event detector 742, and the partition selector752 cannot be accessed via the execution of program instructions, butexclusively by the tamper detector 714 and tamper detection microcode.When a timer interrupt or event trigger occurs, normal operation of thecomputing system is interrupted and the partition selector direct thecontroller 712 to fetch the contents of one or more of the plurality ofpartitions of the BIOS ROM (not shown) via the bus interface 718, whichare provided to the execution logic 706 via TBUS. The contents,including one or more of the corresponding encrypted digital signatures,are provided to the execution logic 706 via TBUS. Therein, the tamperdetection microcode directs the crypto/hash unit 708 to perform a hashof the one or more of the plurality of partitions according to the hashalgorithm that was used by the BIOS manufacturer to generate the one ormore digital signatures. The tamper detection microcode also directs thecrypto/hash unit 708 to decrypt the one or more corresponding encrypteddigital signatures that were fetched from the BIOS ROM using the keystored in the key storage 710. The one or more digital signaturesgenerated by the crypto/hash unit 708, along with the one or moredecrypted digital signatures whose encrypted versions are stored in oneor more specific locations in the BIOS ROM are provided to the tamperdetector 714 via TBUS.

The tamper detector 714 compares one or more pairs of the digitalsignatures. If all comparisons are equal, then the tamper detector 714returns control of the microprocessor to the point at which theevent-based interrupt occurred. If the signatures are not equal, thenthe tamper detector 714 asserts signal SHUTDOWN. The SHUTDOWN signaldirects remaining elements of the microprocessor to power down orotherwise enter a mode that precludes normal operation.

One embodiment contemplates a combined sequence of timer interrupts andevent triggers that is determined by the tamper detection microcode.Another embodiment employs a random number generated by the randomnumber generator 730 at the end of a BIOS check to indicate if a nextBIOS check will be initiated based on a timer interrupt or an eventtrigger. As is discussed above with reference to FIGS. 4-5, the randomnumber generator 730 may be employed, in some embodiments, to randomlyvary the time interval and/or event types and number of events.

In another embodiment, rather than checking a fixed or cyclic number ofthe plurality of partitions, at completion of a BIOS hack check thetamper detection microcode directs the random number generator 730 togenerate a random number which is entered into the partition selector752 to establish a following number of partitions that are to be checkedduring a next BIOS hack check. In this manner, the number of partitionsthat are validated at check point triggers cannot be predicted andprecluded via surreptitious applications executing on themicroprocessor. In a different embodiment, the random number is employedto indicate a next one of the plurality of partitions to be checked.

The elements of the microprocessors according to the present inventionare configured to perform the functions and operations as discussedabove. The elements comprise logic, circuits, devices, or microcode(i.e., micro instructions or native instructions), or a combination oflogic, circuits, devices, or microcode, or equivalent elements that areemployed to execute the functions and operations according to thepresent invention as noted. The elements employed to accomplish theseoperations and functions within the microprocessor may be shared withother circuits, microcode, etc., that are employed to perform otherfunctions and/or operations within the microprocessor. According to thescope of the present application, microcode is a term employed to referto one or more micro instructions. A micro instruction (also referred toas a native instruction) is an instruction at the level that a unitexecutes. For example, micro instructions are directly executed by areduced instruction set computer (RISC) microprocessor. For a complexinstruction set computer (CISC) microprocessor such as an x86-compatiblemicroprocessor, x86 instructions are translated into associated microinstructions, and the associated micro instructions are directlyexecuted by a unit or units within the CISC microprocessor.

Portions of the present invention and corresponding detailed descriptionare presented in terms of software, or algorithms and symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the ones by which those ofordinary skill in the art effectively convey the substance of their workto others of ordinary skill in the art. An algorithm, as the term isused here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, a microprocessor, a central processingunit, or similar electronic computing device, that manipulates andtransforms data represented as physical, electronic quantities withinthe computer system's registers and memories into other data similarlyrepresented as physical quantities within the computer system memoriesor registers or other such information storage, transmission or displaydevices.

Note also that the software (e.g., microcode, firmware, programinstructions, etc.) implemented aspects of the invention are typicallyencoded on some form of program storage medium or implemented over sometype of transmission medium. The program storage medium may beelectronic (e.g., read only memory, flash read only memory, electricallyprogrammable read only memory), random access memory magnetic (e.g., afloppy disk or a hard drive) or optical (e.g., a compact disk read onlymemory (CDROM)), and may be read only or random access. Similarly, thetransmission medium may be metal traces, twisted wire pairs, coaxialcable, optical fiber, or some other suitable transmission medium knownto the art. The invention is not limited by these aspects of any givenimplementation.

The particular embodiments disclosed above are illustrative only, andthose skilled in the art will appreciate that they can readily use thedisclosed conception and specific embodiments as a basis for designingor modifying other structures for carrying out the same purposes of thepresent invention, and that various changes, substitutions andalterations can be made herein without departing from the scope of theinvention as set forth by the appended claims.

What is claimed is:
 1. An apparatus for protecting a basic input/outputsystem (BIOS) in a computing system, the apparatus comprising: a BIOSread only memory (ROM), comprising: BIOS contents, wherein said BIOScontents are stored as plaintext; and an encrypted message digest,wherein said encrypted message digest comprises an encrypted version ofa first message digest that corresponds to said BIOS contents; a tampertimer, configured to periodically generate a BIOS check interrupt thatinterrupts normal operation of the computing system at a prescribedinterval; and a tamper detector, operatively coupled to said BIOS ROMand said tamper timer, configured to access said BIOS contents and saidencrypted message digest upon assertion of said BIOS check interrupt,and configured to direct a microprocessor to generate a second messagedigest corresponding to said BIOS contents and a decrypted messagedigest corresponding to said encrypted message digest using the samealgorithms and key that were employed to generate said first messagedigest and said encrypted message digest, and configured to compare saidsecond message digest with said decrypted message digest, and configuredto preclude said operation of said microprocessor if said second messagedigest and said decrypted message digest are not equal.
 2. The apparatusas recited in claim 1, wherein said BIOS ROM is disposed separately fromsaid tamper timer and said tamper detector on a system board of thecomputing system.
 3. The apparatus as recited in claim 1, wherein saidmicroprocessor employs the Secure Hash Algorithm to generate said secondmessage digest.
 4. The apparatus as recited in claim 1, wherein saidmicroprocessor employs the Advanced Encryption Standard algorithm togenerate said decrypted message digest.
 5. The apparatus as recited inclaim 1, wherein said microprocessor comprises a dedicated crypto/hashunit disposed within execution logic, and wherein said crypto/hash unitgenerates said second message digest and said decrypted message digest,and wherein said key is exclusively accessed by said crypto/hash unit.6. The apparatus as recited in claim 5, wherein said microprocessorfurther comprises a random number generator disposed within saidexecution logic, and wherein said random number generator generates arandom number at completion of a current BIOS check, which is employedby said tamper timer to set a following prescribed interval, wherebysaid prescribed interval is randomly varied.
 7. The apparatus as recitedin claim 5, wherein said key and said tamper timer cannot be accessed byprogram instructions that are executed by said microprocessor.
 8. Anapparatus for protecting a basic input/output system (BIOS) in acomputing system, the apparatus comprising: a BIOS read only memory(ROM), comprising: BIOS contents, wherein said BIOS contents are storedas plaintext; and an encrypted message digest, wherein said encryptedmessage digest comprises an encrypted version of a first message digestthat corresponds to said BIOS contents; and a microprocessor, coupled tosaid BIOS ROM, said microprocessor comprising: a tamper timer,configured to periodically generate a BIOS check interrupt thatinterrupts normal operation of the computing system at a prescribedinterval; and a tamper detector, operatively coupled to said BIOS ROMand said tamper timer, configured to access said BIOS contents and saidencrypted message digest upon assertion of said BIOS check interrupt,and configured to direct said microprocessor to generate a secondmessage digest corresponding to said BIOS contents and a decryptedmessage digest corresponding to said encrypted message digest using thesame algorithms and key that were employed to generate said firstmessage digest and said encrypted message digest, and configured tocompare said second message digest with said decrypted message digest,and configured to preclude said operation of said microprocessor if saidsecond message digest and said decrypted message digest are not equal.9. The apparatus as recited in claim 8, wherein said BIOS ROM isdisposed separately from said tamper timer and said tamper detector on asystem board of the computing system.
 10. The apparatus as recited inclaim 8, wherein said microprocessor employs the Secure Hash Algorithmto generate said second message digest.
 11. The apparatus as recited inclaim 8, wherein said microprocessor employs the Advanced EncryptionStandard algorithm to generate said decrypted message digest.
 12. Theapparatus as recited in claim 8, said microprocessor further comprising:a dedicated crypto/hash unit disposed within execution logic, whereinsaid crypto/hash unit generates said second message digest and saiddecrypted message digest, and wherein said key is exclusively accessedby said crypto/hash unit.
 13. The apparatus as recited in claim 12,wherein said microprocessor further comprises: a random number generatordisposed within said execution logic, and wherein said random numbergenerator generates a random number at completion of a current BIOScheck, which is employed by said tamper timer to set a followingprescribed interval, whereby said prescribed interval is randomlyvaried.
 14. The apparatus as recited in claim 12, wherein said keycannot be accessed by program instructions that are executed by saidmicroprocessor.
 15. A method for protecting a basic input/output system(BIOS) in a computing system, the method comprising: storing BIOScontents as plaintext in a BIOS ROM along with an encrypted messagedigest that comprises an encrypted version of first message digest thatcorresponds to the BIOS contents; periodically generating a BIOS checkinterrupt that interrupts normal operation of the computing system at aprescribed interval; upon assertion of the BIOS check interrupt,accessing the BIOS contents and the encrypted message digest, andgenerating a second message digest corresponding to the BIOS contentsand a decrypted message digest corresponding to the first encryptedmessage digest using the same algorithms and key that were employed togenerate the first message digest and the encrypted message digest;comparing the second message digest with the decrypted message digest;and precluding operation of the microprocessor if the second messagedigest and the decrypted message digest are not equal.
 16. The method asrecited in claim 15, further comprising: separately disposing the BIOSROM on a system board of the computing system.
 17. The method as recitedin claim 15, wherein said accessing comprises: employing the Secure HashAlgorithm to generate the second message digest.
 18. The apparatus asrecited in claim 15, wherein said accessing further comprises: employingthe Advanced Encryption Standard algorithm to generate the decryptedmessage digest.
 19. The method as recited in claim 15, wherein themicroprocessor comprises a dedicated crypto/hash unit disposed withinexecution logic, and wherein the crypto/hash unit generates the secondmessage digest and the decrypted message digest, and wherein the key isexclusively accessed by the crypto/hash unit.
 20. The method as recitedin claim 15, wherein the microprocessor further comprises a randomnumber generator disposed within the execution logic, and wherein therandom number generator generates a random number at completion of acurrent BIOS check, which is employed by the tamper timer to set afollowing prescribed interval, whereby the prescribed interval israndomly varied.
 21. The method as recited in claim 19, wherein the keycannot be accessed by program instructions that are executed by themicroprocessor.